Diesel engines have long been used in automotive application, particularly for larger truck applications. Because of the great popularity of diesel engines and extensive use with trucks on the highways and roads around the world, there have been tremendous efforts and great advances to reduce many air polluting emissions entering the environment as much as practical.
Of the various emissions which have been identified for possible reduction, oxides of nitrogen commonly referred to as NOx emissions have been regulated by the United States Federal government. It has been known that selective catalytic reduction (SCR) is a very effective means to provide NOx reduction. Selective catalytic reduction has been known for stationary power applications. Selective catalytic reduction uses an aqueous urea solution as a reductant introduced into the exhaust system upstream of the catalytic converter.
One of the hurdles in using such an aqueous urea solution is that it is subject to freezing. For example, a 32% urea solution may freeze at temperatures below −11° C. This relatively modest cold temperature is often encountered in colder climates during the winter season. If the urea solution freezes, it will not function in its desired manner as a reductant nor will it freely flow to the reduction site where it can be warmed by the hot exhaust emissions. Besides running with elevated emissions, an engine may run afoul of certain regulations without the liquid urea.
It is desirable to apply such a SCR system to automotive applications. Such SCR systems work fine in warm climates or while the diesel engine is running and the heat of the engine and exhaust provides for sufficient heat to keep the reducing solution in liquid state and freely flowing to the site of reduction. Maintaining the solution above freezing while the engine is running is provided by using warmed coolant of the engine to heat the reservoir and the urea supply lines. It is also know to apply an electric heater fed from the engine battery.
While these solutions are acceptable during operation of the diesel engine when the coolant is heated by the engine and the battery is being recharged by the alternator, they are not adequate for long storage or overnight shut down of the diesel engine in cold weather.
Previous attempts at providing liquid urea after long shut down and subsequent cold start of the diesel was to provide a separate small starting tank where the small amount of urea can be thawed during the initial start up of the engine or preheated by an electrical heater. This starting volume is used during the time it takes the diesel engine to warm up and use its warmed coolant to warm and thaw the main tank of urea solution. Such a remedy is expensive requiring an extra tank, and relies on the premise that the amount of starting urea solution is sufficient while the main tank is warmed and thawed. This premise may not be justified during extreme cold weather starts which can result in a phase of engine operation when there is no thawed or liquid reductant available.
It is also well known that diesel engines are harder to start than regular gasoline engines in cold weather. Accordingly, it is common to provide an auxiliary engine block electric heater to a diesel engine for keeping the engine warm when it is shut off for an extended period of time such as overnight in cold climates. Such heaters are commonly available and can be installed as original equipment or can be provided as an aftermarket option. A typical heater includes an electric heating element installed in the water jacket of the engine. A power supply cord plugs into an available 120 volt AC electric outlet. These heaters are widely used because they effectively warm the engine sufficiently to provide a reliable cold start. Truck drivers are used to plugging these heaters in during the winter season for a better cold weather start.
What is needed is a modified auxiliary engine block heater that also incorporates a heating element mounted in the urea tank such that when the heating element of the diesel engine is on, the urea tank is also automatically warmed to keep the solution from freezing. What is also needed is a heater system for a SCR system that does not entail any additional procedures other than those with which a truck operator is already familiar.